The present invention relates to an infrared heater, and more particularly to an infrared heater which emits far-infrared rays having a way length of 4.about.25 .mu.m for use in effecting reflowing of solder, curing of resins, drying of food, heating of wood an wet coatings, warming for medical treatment, and the like.
Recently, there is a general trend for electronic equipment to be made increasingly compact and lightweight. Accordingly, printed circuit boards having a large number of electronic parts mounted in a limited area (hereunder referred to as "high-density boards" or "high-density printed circuit boards") are widely used. In the manufacture of high-density boards, it is necessary to supply heat to a narrow area between electronic parts on the high-density board in order to reflow a paste solder or cure an adhesive resin when the electronic parts are connected to the circuit board using a paste solder or a resinous bonding agent. As an industrial heating apparatus for these purposes, a reflow furnace is used in which infrared heaters are placed on the top and bottom walls of a tunnel-type heating zone. The infrared heater used in the reflow furnace comprises a sheath heater and an infrared radiation panel made of a surface-treated stainless steel plate which is disposed over the sheath heater.
However, such conventional infrared heaters do not emit a sufficient amount of heat, so they must be operated at high power in order to thoroughly heat electronic parts on the board. This is not desirable from the viewpoint of economy, because the service life is very short when the heaters are operated at high power. Alternatively, a large-sized heater can be employed in order to increase the heat supply, but such a larger-sized heater is uneconomical because it requires an increase in the size of the reflow furnace.